Characterisation of mineralisation of bone and cartilage: X-ray diffraction and Ca and Sr Kα X-ray fluorescence microscopy

Bone is a dynamic structure, constantly remodelling in response to changing mechanical and environmental factors. This is particularly evident in the mineral component encrusting the collagenous framework. The mineral is principally in the form of calcium apatite, but calcium can exchange with strontium, both during the cellular processes of mineralisation and resorption and by passive exchange with the deposited crystals. Mineralisation is generally characterized by densitometry, but because of the differences in absorption cross sections of calcium and strontium it can be misleading in studies of composition. In this work we have used X-ray diffraction to identify calcium and strontium apatite and X-ray fluorescence to quantify strontium and calcium distribution. With the beam characteristics available from synchrotron radiation, this has enabled us to obtain microscopic resolution on thin sections of bone and cartilage from the equine metacarpophalangeal joint. Two issues have been investigated; the first is the distribution of mineral in the bone-cartilage interface and within individual trabeculae. In trabecular bone the ratio of strontium to calcium concentration was typically 0.0035 ± 0.0020, and higher by a factor of ∼3 at the periphery than in the centre of a trabeculum (possibly reflecting the more rapid turnover of mineral in the surface layer). In the dense subchondral bone the ratio was similar, approximately doubling in the calcified cartilage. The second objective was to explore the changes in mineralisation associated with development of osteoarthrosis. We analysed lesions showing cartilage thinning and changes in the trabecular organization and density of the underlying bone. At the centre of the lesion the ratio of strontium to calcium was much lower than that in normal tissue, although the calcified cartilage still showed a higher ratio than the underlying bone. In the superficially normal tissue around the lesion the calcified cartilage returned to a normal ratio much more rapidly than the underlying bone. These data demonstrate the complex relationship between changes in cartilage and the underlying bone.     

Oxidation kinetics of magnesium alloys treated by tantalum ions implantation

AZ31 magnesium alloys were implanted with tantalum ions with doses of 1 × 10¹⁶, 5 × 10¹⁶ and 1 × 10¹⁷ ions/cm², using a metal vapor vacuum arc (MEVVA) at an extraction voltage of 45 kV. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analysis suggested that tantalum ions implantation promoted the formation of the pre-oxidation layer and a new Ta₂Al phase was formed in the implanted layer. Then, the oxidation kinetics of the implanted specimens was investigated by isothermal oxidation at 773 K in pure O₂ up to 90 min. The results showed that after implantation treatments the oxidation resistance of the specimens was significantly improved and the specimen with the highest dose had the best oxidation resistance. Finally, the mechanism of the anti-oxidation effects was also discussed.     

A study on bactericidal properties of Ag coated carbon nanotubes

A silver layer is coated on carbon nanotubes (CNTs) by ion beam assisted deposition (IBAD). Standard agar dilution method is used to evaluate the bactericidal rate against Gram positive S. aureus and negative E. coli. The structure and the chemical states are investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that Ag coated CNTs possess very high bactericidal rate. In comparison with the Ag coated pyrolytic carbon sample, the Ag coated CNTs show stronger bactericidal property.     

Analytical investigations of irradiated inert matrix fuel

Yttria stabilised zirconia (YSZ) inert matrix fuel (IMF) fabricated at PSI and irradiated 3 years in the Halden Material Test Reactor (HBWR) since 2000, has been examined by Electron Probe Microanalysis (EPMA) and Secondary Ion Mass Spectroscopy (SIMS) after irradiation and compared with data gained for the unirradiated material. The examined pellet cross-section was estimated to have an equivalent burn-up of 22 MW d kg⁻¹. EPMA measurements demonstrate that the burn-up was rather flat over more than the half pellet radius. A Pu consumption of about 2.5 wt% has been measured with a higher rate in the fuel border zone. The high fuel temperature is responsible for a certain homogenisation of the mineral phases in the fuel centre region whereas the border zone has remained rather with an as-fabricated phase distribution. The central part was also characterised by a dense porosity distribution as well as a temperature and relocation driven depletion of the volatile fission products Xe and Cs. In addition, SIMS has been realised on the same specimen in order to determine the semi-quantitative distribution of different isotopes in the pellet.     

A method for the quantification of total xenon concentration in irradiated nuclear fuel with SIMS and EPMA

A new method for the quantitative determination of the total xenon concentration in irradiated nuclear fuel is presented. The SIMS measurement of xenon enables the detection of the gas filling bubbles which are not detected with EPMA. The quantification is achieved using the EPMA data as reference at position where no or nearly no bubbles are detected. A new approach using the complementary information given by EPMA, SEM and SIMS is proposed, it opens new horizons for the characterisation of fission gases in irradiated nuclear fuel.     

Irradiation damage of uridine molecules with MeV heavy ions

In order to study the mechanism of the nucleotide directly damaged by energetic heavy ions, the residual ratio of uridine molecules after irradiation was measured by means of High Performance Liquid Chromatography (HPLC). The experimental results show that the irradiation damage probability depends on the electronic energy loss rate (S_e) of incident ions: first it increases quickly with S_e, then becomes stable when S_e reaches 800 eV/nm. The contribution of the nuclear collisions can be neglected compared with that of the electronic process. This is not only because that the nuclear energy loss rate (S_n) is much smaller than S_e for MeV heavy ions, but also because the energy deposition through the electronic process is more efficient in damaging molecules than through the nuclear process.     

Modeled salt density for nuclear material estimation in the treatment of spent nuclear fuel

Spent metallic nuclear fuel is being treated in a pyrometallurgical process that includes electrorefining the uranium metal in molten eutectic LiCl-KCl as the supporting electrolyte. We report a model for determining the density of the molten salt. Material balances account for the net mass of salt and for the mass of actinides present. It was necessary to know the molten salt density, but difficult to measure. It was also decided to model the salt density for the initial treatment operations. The model assumes that volumes are additive for the ideal molten salt solution as a starting point; subsequently, a correction factor for the lanthanides and actinides was developed. After applying the correction factor, the percent difference between the net salt mass in the electrorefiner and the resulting modeled salt mass decreased from more than 4.0% to approximately 0.1%. As a result, there is no need to measure the salt density at 500 °C for inventory operations; the model for the salt density is found to be accurate.     

The influence of carbon ion irradiation on sweet sorghum seeds

The aim of this study is to investigate the effects of different doses of 100 MeV/u carbon ions on sweet sorghum seeds in order to improve crop yields and their sugar content. After irradiation, seeds were germinated and grown to 30 days, and others were sown in the field. At the end of harvesting season all planted seeds were picked separately and M2 generations obtained. The differences among the treatments were examined using the RAPD procedure. In the study done by using 38 primers; according to the amplification results, the differences among the various doses treatment were shown.     

Experimental study of the Ho(d, 2n) and Ho(d, p) nuclear reactions up to 20 MeV for production of the therapeutic radioisotopes Er and Ho

The radioisotope ¹⁶⁵Er (T_1/2 = 10.36 h) is a candidate for Auger-electron therapy. The β⁻-emitting ^166gHo (T_1/2 = 26.83 h) is now being explored for various therapeutic applications. In the frame of our systematic study of charged particle production routes of therapeutic radionuclides the excitation functions of the ¹⁶⁵Ho(d, 2n)¹⁶⁵Er and ¹⁶⁵Ho(d, p)^166gHo reactions were measured up to 20 MeV by using a stacked foil irradiation technique and X/γ-ray spectroscopy. The excitation function of the ¹⁶⁵Ho(d, 2n)¹⁶⁵Er reaction was measured for the first time while for the ¹⁶⁵Ho(d, p)^166gHo reaction only a single dataset of earlier measured cross-sections was found. The measured excitation functions were compared to the results of different nuclear reaction model codes. The calculated thick target yield of the ¹⁶⁵Ho(d, 2n) reaction is significantly higher over the optimal energy range than that for the ¹⁶⁵Ho(p, n) reaction investigated earlier by us. The integral yield of the ¹⁶⁵Ho(d, p)^166gHo reaction is rather low compared to the established ¹⁶⁵Ho(n, γ)¹⁶⁶Ho reaction in a nuclear reactor.     

Status of the problem of nuclear cross section data for IBA

The progress achieved in an IAEA Coordinated Research Project (CRP) to improve the cross section data for IBA is reported. The objective of the CRP, started in 2005, is to create a nuclear cross section database for IBA that contains reliable and usable data freely available to the entire IBA community. The major results achieved so far by the CRP participants are discussed. The results include compilation and assessment of the existing cross sections, new experimental data and evaluation of the most wanted cross sections. The experimental results are incorporated into the IBANDL database (www-nds.iaea.org/ibandl/) and evaluated data are presented at the SigmaCalc cross section calculator (www-nds.iaea.org/sigmacalc/).     

Immobilization of Rhodococcus erythropolis B4 on radiation crosslinked poly(vinylpyrrolidone) hydrogel: Application to the degradation of polycyclic aromatic hydrocarbons

A poly(vinylpyrrolidone) (PVP) hydrogel crosslinked by gamma radiation was used to immobilize, by adsorption, Rhodococcus erythropolis B4 strain. Immobilized cells were tested for their capacity to degrade naphthalene and anthracene, under aerobic conditions.The results showed that, the strain fixed is capable of growing in the presence of naphthalene or anthracene as a unique source of carbon. It was also shown that, the fixed strain can be preserved by freeze-drying for further use. The biodegradation capacity was improved during the second use.     

Evaluated activation cross sections of longer-lived radionuclides produced by deuteron induced reactions on natural titanium

Selected charged particle induced reactions are used to monitor the actual parameters of bombarding particle beams. One of these reactions is ^natTi(d, x)⁴⁸V for which recommended cross section data are available in one of the databases of the International Atomic Energy Agency (http://www-nds.iaea.or.at/medical/). This database contains all together 22 monitor reactions for practical applications covering energy up to 100 MeV depending on the reactions. In the case of the ^natTi(d, x)⁴⁸V reaction recommended data are given in the 9-50 MeV energy interval because at the time of creation not precise enough experimental data were available to recommend values from threshold up to 9 MeV. In this work we measured the excitation function in this relevant low energy range, collected new experimental data and suggest high confidence recommended values for the missing low energy part of the monitor excitation function.     

Evaluated activation cross sections of longer-lived radionuclides produced by deuteron induced reactions on natural iron up to 10 MeV

Charged particle induced reactions can be used to monitor in real time the wear of mechanical structures such as internal combustion engines and turbines. Charged particle induced reactions with suitable properties also can be used for monitoring the actual parameters of bombarding particle beams. One of these reactions is the ^natFe(d,x)⁵⁷Co process. The available experimental data in the literature are well established around and above the maximum of the excitation function, however only a little, scattered data are available in the threshold energy region of the reaction. In this work we measured the excitation functions of relevant processes resulting in ^55,56,57,58Co, ⁵⁹Fe and ^52,54Mn induced by deuteron beams on natural iron in the energy range from threshold up to 10 MeV. The new experimental data collected are used to determine with high confidence recommended values for the missing low energy part of the investigated excitation functions.     

Fragmentation of water on swift He ion impact

Charge exchange and fragmentation are the usual results in ion-molecule collision systems, and the specifics of the fragmentation process determine the chemical destiny of the target system. In this paper, we report recent progress on calculations of the fragmentation patterns for the model system He²⁺ + H₂O for projectile energies of a few keV. The calculations are obtained using the electron-nuclear dynamics (END) method for solution of the time-dependent Schrödinger equation.     

Molecular dynamics simulation of the pressure-volume-temperature data of xenon for a nuclear fuel

The exact equation of state for the fission gas is necessary for the accurate prediction of the fission gas behavior in a nuclear fuel. However, certain kinds of extrapolating data are used to construct and verify the equations of state for the fission gas because experimental data are very limited at high temperatures and pressures that are encountered in the nuclear fuel. To fill the lack of experimental data for the fission gas, the behavior of Xe gas atoms was investigated by molecular dynamics simulation assuming an exponential-six potential. The molecular dynamics simulation produced reasonable pressure-volume-temperature data for Xe and the simulation results were compared with existing equations of state for Xe.     

Study of substrate topographical effects on epithelial cell behavior using etched alpha-particle tracks on PADC films

Micrometer-size pits on the surface of a polymer (polyallyldiglycol carbonate or PADC) substrate created by alpha-particle irradiation and subsequent chemical etching were used to study the topographical effects alone on cell behavior. Vinculin, the cell adhesion and membrane protrusion protein, was used as an indicator of cytoskeletonal reorganization on the substrate and localization of vinculin was used to demonstrate the presence of focal adhesions. In our experiments, vinculin expressed in epithelial HeLa cells cultured on PADC films with track-etch pits, but not in cells cultured on the raw or chemically etched blank films. In other words, vinculin expression was induced by the topography of track-etch pits, while etching of the substrate alone (without alpha-particle irradiation) did not cause up-regulation of vinculin protein expression. HeLa cells cultured on PADC films with track-etch pits also showed changes in cell proliferation, cell area and cell circularity, and were largely contained by the pits. In other words, the cell membrane edges tended to be in contact with the pits. By comparing the correlation between the positions of HeLa cells and the pits, and that between the positions of cells and computer-simulated pits, the tendency for membrane edges of HeLa cells to be in contact with the pits was recognized. This could be explained by inhibition of membrane protrusion at the pits. In conclusion, substrate track-etch pits were an important determinant of epithelial cell behaviors.     

聚变裂变混合乏燃料焚烧堆FDS-SFB燃料循环方案设计与分析

针对聚变裂变混合乏燃料焚烧堆FDS-SFB(Spent Fuel Burner),基于湿法和干法两种后处理技术途径提出了不同的燃料循环方案。并分别对FDS-SFB燃料循环所需的初装资源量、燃料制备和乏燃料后处理能力进行初步质量流分析和可行性初步评估。基于较好嬗变和增殖性能的FDS-SFB典型中子学方案的质量流初步分析表明:两种方案燃料循环其所需的初装资源量、燃料制备、乏燃料后处理能力具有初步的可行性。     

Experimental setup for studying the effects of alpha particles on zebrafish embryos

In the present work, we have studied the feasibility to use an experimental setup based on polyallyldiglycol-carbonate (PADC) films to study effects of alpha particles on dechorionated zebrafish embryos. Thin PADC films with a thickness of 16 μm were prepared from commercially available CR-39 films by chemical etching and used as support substrates for holding zebrafish embryos for alpha-particle irradiation. These films recorded alpha-particle hit positions, quantified the number and energy of alpha particles actually incident on the embryo cells, and thus enabled the calculation of the dose absorbed by the embryo cells. Irradiation was made at 4 h post fertilization (hpf) with absorbed doses up to 2.3 mGy. Images of the embryos at 48 hpf were examined for identification of morphologic abnormalities. The preliminary results showed that absorbed doses corresponding to the abnormally developed embryos ranged from 0.41 to 2.3 mGy, which was equivalent to 0.21-1.2 mGy in human.     

Micro-PIXE-RBS methods highlighting the influence of phosphorus on the in vitro bioactivity of sol-gel derived glass particles in the SiO2-CaO-P2O5 system

Ion beam analysis methods were used to characterize the interface of bioactive glasses with surrounding biological fluids. Glass particles in the SiO₂-CaO and SiO₂-CaO-P₂O₅ compositions were made by sol-gel processing and soaked in biological fluids for periods up to 4 days. The surface changes were characterized using PIXE-RBS, which are efficient methods for multielemental analysis and accurate trace elements quantification. Elemental maps of major and trace elements were obtained at a micrometer scale and revealed the bone bonding ability of the materials. Glass particles are quickly coated with a thin calcium phosphate-rich layer containing traces of magnesium. After a few days, SiO₂-CaO-P₂O₅ glass particles are entirely changed into calcium phosphates, whereas SiO₂-CaO particles exhibit a different behavior: the previously Ca-P enriched periphery has been dissolved and glass particles consist of a silicate network. Calculation of the Ca-P atomic ratios at the glass/biological fluids interface provides us with an explanation for this: an enduring apatitic phase seems to be formed at the periphery of SiO₂-CaO-P₂O₅ glass particles. Presence of phosphorus in the glass matrix thus has an influence on the amplitude and the kinetics of reaction of the bioactivity process. It might result in an improved chemical bond with living tissues.     

Experimental studies on positronium negative ions

Recently, a new stage of experimental studies on positronium negative ions has begun. This is due to the development of a new detection method and the discovery of the ion formation at metal surfaces. In the present paper, experimental studies are reviewed and future experiments are proposed.